1. Field of the Invention
This invention relates to an apparatus for opening constricted or closed blood vessels with a tubular flexible catheter. In particular, the invention relates to an improved angioplasty catheter.
2. Description
Methods of dilating blood vessels by means of catheters are usually referred to as angioplasty. Corresponding catheters are accordingly referred to as angioplasty catheters.
When blood circulation in a patient is interrupted due to an arteriosclerotic lesion or inclusion, frequently an operation can be performed to bypass the interruption. Recently blood vessels have been opened by angioplasty techniques with increasing success. The first angioplasty methods were based on simple dilation of a constriction by means of a balloon catheter which dilated the constriction at relatively high pressure. The disadvantage of this method is that after the balloon catheter is removed the blood vessels partially yield to pressure elastically and subsequently resume their old constricted shape in a relatively short time. The construction returns and the opening of the constriction therefore is not permanent.
ln other methods, some of the deposits causing the constriction is removed. This is always necessary should there be an almost complete blockage of the vessel. Both mechanical methods and methods using laser beams have been proposed for this purpose.
DOS No. 32 42 341 describes a catheter, the distal end of which has an expanding head comprising one or more scrapers of resilient material which can be opened by means of a cable attached to a handle disposed at the proximal end of the catheter. The inclusion or deposit can be eliminated with this apparatus by scraping movements. The scrapings from the deposit are carried off by spiral conveyor located inside the catheter. The disadvantage of this apparatus is that the scrapers come into contact with the blood vessel walls and may damage them. There is also a risk that the scrapings may be washed away into the bloodstream if the conveyor inside the catheter does not work effectively. Embolisms, thus, may occur.
The principle of methods using laser beams is to burn a passage through the constriction in the blood vessel. The disadvantage of this method is that the inner surface of the passage burnt through the construction remains relatively rough and therefore tends rapidly to become blocked again.